Reproductive Energetics and Physiology of the Desert-Nesting Gray Gull, Larus modestus

Abstract

Seagulls (Larus, Laridae, Charadriiformes) are one of the most cosmopolitan of avian genera. Their 44 species occupy a wide diversity of habitats between 80° north and 80° south latitude (Harrison 1983). Found from sea level along the coasts of each continent and shores of most islands, to the highest Andean lakes, larids inhabit and reproduce under extremely varied ambient conditions, several in some of the most interesting, challenging, and remote areas on earth. Among those, the gray gull, Larus modestus, is truly unique. Dispersed from 0° to 40° south latitude along the Pacific coast of South America during the austral winter, gray gulls congregate during their August to February breeding-nesting season on the coast of northern Chile between Arica (18° S) and Tatal (26° S), where they court, mate, and feed but do not nest. Instead, unlike most other congeners, they nest far from food and water on the barren pampas of the Atacama (Goodall et al. 1945; Howell et al. 1974; Guerra et al. 1988a), a desert so desolate that Moffett (1969) characterized it as “biologically bankrupt.” Nesting in the waterless pampas, as far as 100 km from the coast (Guerra et al. 1988a) between 22° and 24° south latitude (Fig. 1), exposes the gray gulls to intense solar radiation and extreme diurnally-variable ambient conditions (e.g., ground temperature = 2° to 61°C, air temperature = 2.5° to 38°C, wind = 0 to 55 km/h; Howell et al. 1974; Fitzpatrick and Guerra 1988; Guerra et al. 1988a) and requires them to commute long distances for food and water.